HomeNewsHow to use laser cloaking to hide Earth from remote detection by aliens

How to use laser cloaking to hide Earth from remote detection by aliens

NASA's Kepler telescope detects habitable exoplanets by watching for tiny dips in the light from stars. What if aliens have the same idea when observing our Sun?

April 1, 2016

A 22W laser used for adaptive optics on the Very Large Telescope in Chile. A suite of similar lasers could be used to cloak our planet’s transit around the Sun. (credit: ESO/G. Hüdepohl)

We could use lasers to conceal the Earth from observation by an advanced extraterrestrial civilization by shining massive laser beams aimed at a specific star where aliens might be located — thus masking our planet during its transit of the Sun, suggest two astronomers at Columbia University in an open-access paper in Monthly Notices of the Royal Astronomical Society.

The idea comes from the NASA Kepler mission’s search method for exoplanets (planets around other stars), which looks for transits (a planet crossing in front a star) — identified by a tiny decrease in the star’s brightness.*

To detect exoplanets, NASA’s Kepler measures the light from a star. When a planet crosses in front of a star, the event is called a transit. The planet is usually too small to see, but it can produce a small change in a star’s brightness of about 1/10,000 (100 parts per million), lasting for 2 to 16 hours. (credit: NASA Ames)

Kepler has confirmed the existence of more than 1,000 planets using this technique, with tens of these worlds similar in size to the Earth. Kipping and Teachey speculate that alien scientists could use this approach to locate Earth, since it’s in the “habitable zone” of our Sun (a distance where the temperature is right for liquid water, so it may be a promising place for life), and may be of interest to aliens.*

How to cloak our Earth from aliens

Columbia Professor David Kipping and graduate student Alex Teachey suggest that transits could be masked by controlled laser emission, with the beam directed at the star where the suspected aliens might be located. When the planet’s transit takes place, the laser would be switched on to compensate for the dip in light.**

Illustration (not to scale) of the transit cloaking device. To cloak the Earth, a laser beam (orange) is fired from the night side of the Earth (blue circle) toward a target star (“receiver”) during the transit. (credit: David M. Kipping and Alex Teachey/MNRAS)

According to the authors, emitting a continuous 30 MW laser for about 10 hours, once a year, would be enough to eliminate the transit signal, at least in the visible-light range. The energy needed is comparable to that collected by the International Space Station solar array in a year. A chromatic (multi-wavelength) cloak, effective at all solar wavelengths, is more challenging, and would need a large array of tuneable lasers with a total power of 250 MW.***

“Alternatively, we could cloak only the atmospheric signatures associated with biological activity, such as oxygen, which is achievable with a peak laser power of just 160 kW per transit. To another civilization, this should make the Earth appear as if life never took hold on our world”, said Teachey.

Cool Worlds Lab/Columbia University | A Cloaking Device for Planets

Broadcasting our existence: the METI (message SETI) approach

The lasers could also be used to broadcast our existence by modifying the light from the Sun during a transit to make it obviously artificial, such as modifying the normal “U” transit light curve (the intensity vs. time pattern during transit). The authors suggest that we could even transmit information by modulating the laser beams at the same time, providing a way to send messages to aliens.

Perhaps aliens have had the same thought. The two astronomers propose that the Search for Extraterrestrial Intelligence (SETI), which currently looks mailing for alien radio signals, could be broadened to search for artificial star transits. Such signatures could also be readily searched in the NASA archival data of Kepler transit surveys.

* Once detected, the planet’s orbital size can be calculated from the period (how long it takes the planet to orbit once around the star) and the mass of the star using Kepler’s Third Law of planetary motion. The size of the planet is found from the depth of the transit (how much the brightness of the star drops) and the size of the star. From the orbital size and the temperature of the star, the planet’s characteristic temperature can be calculated. From this, the question of whether or not the planet is habitable (not necessarily inhabited) can be answered. — Kepler and K2, NASA Mission Overview

** It’s not clear what indicators might lead to such a suspicion, aside from a confirmed SETI transmission detection. It would be interesting to calculate the required number and locations of lasers, their operational schedule, and their power requirements for a worst-case scenario — assuming potential threats from certain types of stars, or all stars — considering laser beam divergence angle, beam flux gradients, and maximum star distance within about one degree of a planet’s ecliptic plane can see it transit in the ecliptic plane, based on assumed maximum alien telescope resolving power.

[UPDATE 1/3/2016: from Kipping regarding beam divergence angle, flux gradients, and primary focus of the paper]: “Beam shaping, through the use of multiple beams, can produce effectively isotropic radiation within the beam width. Unless the target is very close, the beam width typically encompasses the entire alien solar system by the time it reaches, due to beam divergence. So we don’t even really need to know the position of the target planet that well (although we likely do anyway thanks to our detection methods). A common misunderstanding of our paper is to erroneously assume that we are advocating that humanity should build this for the Earth, but actually we are pointing out that if even our current technology can pull off a pretty effective cloak then other more advanced civilizations may be able to hide from us perfectly.”]

The transit method is presently the most successful planet discovery and characterization tool at our disposal. Other advanced civilizations would surely be aware of this technique and appreciate that their home planet’s existence and habitability is essentially broadcast to all stars lying along their ecliptic plane. We suggest that advanced civilizations could cloak their presence, or deliberately broadcast it, through controlled laser emission. Such emission could distort the apparent shape of their transit light curves with relatively little energy, due to the collimated beam and relatively infrequent nature of transits. We estimate that humanity could cloak the Earth from Kepler-like broadband surveys using an optical monochromatic laser array emitting a peak power of ∼30 MW for ∼10 hours per year. A chromatic cloak, effective at all wavelengths, is more challenging requiring a large array of tunable lasers with a total power of ∼250 MW. Alternatively, a civilization could cloak only the atmospheric signatures associated with biological activity on their world, such as oxygen, which is achievable with a peak laser power of just ∼160 kW per transit. Finally, we suggest that the time of transit for optical SETI is analogous to the water-hole in radio SETI, providing a clear window in which observers may expect to communicate. Accordingly, we propose that a civilization may deliberately broadcast their technological capabilities by distorting their transit to an artificial shape, which serves as both a SETI beacon and a medium for data transmission. Such signatures could be readily searched in the archival data of transit surveys.

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Response from Seth Shostak of SETI regarding the concept that ET might optically distort its transit profile to serve as either a beacon or for cloaking:

“Of course what you suggest is possible, and it has the advantage of producing an everlasting, always present ‘message.’ But it’s pretty much only a one-bit message (“we’re here”), and if you’re going to communicate across light-years, where just exchanging ONE message takes many years, I’d be surprised if the aliens would go for such a meager missive!”

Any civilization that ponders doing this would have to consider that their planet is already in someone else’s catalog of thousands of planets with visible transits and interesting atmospheres. If their planet suddenly disappears from view, then they might qualify as REALLY interesting. Better to broadcast gradually strengthening signs of life averse elements, if one wants to play the cloaking game.

This is yet another dystopian fantasy. “plunder our planet’s resources”? No, there are far more resources, excepting life itself, in the asteroid belt, the Kuiper Belt and the Oort Cloud than could be found if they exploded the Earth for raw materials.

If they were seeking usable lands to occupy, they would get far more usable lands by building space colonies from asteroidal resources than by inhabiting planets. Since we knew this in the 20th century, they surely know it as well.

“an advanced alien civilization might wipe out the human race the way a person might wipe out a colony of ants.” MIGHT they do this? Sure, but why would they want to? The only unique assets Earth offers are our life forms and our cultures.

Aliens could take 100 specimens of any terrestrial life form and then breed as many of that species as they desired. As to our cultures, those only continue to exist when left alone. Anthropologists study cultures; they don’t wipe out cultures.

We should stop wasting time thinking about such fantasies and start thinking about the very real and imminent threat that accelerating automation, via its handmaiden technological unemployment, will pose to all human societies in the 2020s. We need to start testing new, abundance-based societal models before mass unemployment disrupts our existence.

Humdinger of an issue, even for KurzweilAI.net. First, we have a 10 year-long project to get to where we next can try to image 1 cubic millimeter of mouse brain (for another $18m or so). Next, we have a Star-Trek drug-making machine that would probably be outlawed (to protect us). And here, a major laser array running 24/7 to either advertise inside or to obfuscate the entire light cone the Earth projects as a shadow as it circles the sun. Not sure how either would differ to alien eyes.

Exciting to anticipate but hard to imagine how the next exciting issue is going to top all of that good stuff – exponentially, of course! :-}

hilarious. I mean for starters the laser = technology = civilization -even if only robotically. however we have been literally broadcasting our existence through radio waves and then television for nearly a century. = 100 light years and expanding. sounds like someone wants some research money and created a non existent problem to be solved with an silly solution.

Radio and TV are buried in the cosmic noise. I suggest you read the updated ** footnote for the real purpose of this story. Hint: has anyone examined the Kepler exoplanet data for coherent light patterns that may block signs of Kardashev scale type I or higher civs?

I’m afraid even the Huffington Post Science section beat us all on this news item … :-} (though admittedly I don’t think they mentioned Kardashevian civilizations … probably not close enough to being Kardashian …)

It seems obvious some other Race that is or could be many Light Years ahead of us in technology would be able to detect any signs of something as simple as a laser. Also would be able to cover up any signs it did not want us to know about. Why is it we persist in thinking we are the all knowing ones?
Just my opinion. Larry

I hope we one day find someone else out there…. let’s remind everyone just how far away everything is…. and if anyone could crack the mysteries of the universe to be able to build spaceships and hack their DNA code to survive in deep space and have near unlimited energy or resources to travel great distances or do so over great time periods, the last thing we would have to worry about is them coming here, or taking anything from us The ultimate resource is Knowledge and they likely can’t take that from some minor civilization that is still debating global warming, or fighting with our lizard brains about politics or region or just trying to hop over 1 planet to find out for sure if there was ever life there. The worry should be it takes far too long to send even a single message between each other to say Hello. We can’t even come up with a solid theory on what the majority of the Universe is made of or how it works (dark matter or dark energy)…. or are we moving apart or all ending up at the Great Attractor.

With our Earthly radio and later TV or other signals traveling at the speed of light for about 200 years ahead of any effort to cloak it later with laser light, I am thinking Aliens will be smarter than our current best cloaking ideas. My guess is as any civilization develops it happens in a similar way on their planet too…. that no one thinks to cloak it first (or has the technology 200 years earlier), so how do you get 200 light years ahead of your older signals?. Anyone who is afraid of aliens has spent more time influenced by fear based movie plots vs. common sense or physics as we know it.

While we are on the subject of invading aliens.. it really bothers me that of all intelligent people that Stephen Hawking is used as the tip of the spear in any argument about what we should be afraid of. I think the quotes came from this interview posted here:

Question: You recently launched a very ambitious initiative to search for intelligent life in our galaxy. A few years ago, though, you said it would be better not to contact extraterrestrial civilizations because they could even exterminate us. Have you changed your mind?

Answer: If aliens visit us, the outcome could be much like when Columbus landed in America, which didn’t turn out well for the Native Americans. Such advanced aliens would perhaps become nomads, looking to conquer and colonize whatever planets they can reach. To my mathematical brain, the numbers alone make thinking about aliens perfectly rational. The real challenge is to work out what aliens might actually be like.

What I always liked about Hawking was his ability to study where we are right now in time and space and then think backwards, using logic and his knowledge of physics to reverse engineer all the single/likely steps it would take to get to the very beginning… the big bang. I find it sad that he can’t do exactly that going forward along a logical path of what any civilization (alien or us) would need to do to survive from the spark of life up to the intelligent being, then the creation of machines and then computers and then escape their own home planet to then live among the stars. You can’t just decode one or two required secrets of the universe, but you need hundreds of ways to outsmart physics to survive and prosper beyond the bubble of your home planet. You can’t really skip any steps and when you put that all together you realize that by the time you have all the resources to do that, the last thing you need is to go thousands (or billions) of light years away to then take less resources away from someone else (makes NO logical sense!). Of course Hawking is correct that IF an alien species did show up we would be so outmatched, that we could not even put up a fight… I think Hawking should have compared humans to ants vs. Europeans to the Natives… actually maybe Hawking should have compared Natives vs. viruses … No never mind, the Natives were killed off by their lack of exposure to the same viruses the Europeans were over generations, so actually viruses did wipe out millions of humans (War of the Worlds joke goes here somewhere). But I got off subject….

Anyhow… I publicly call out Hawking to a debate just how silly and ridiculous it would be to truly be afraid of any alien species from a distant galaxy, or even just a few solar systems over. And why they will NEVER, ever visit us in person… EVER. Any fear based discussion is a complete mathematical failure to comprehend distances and understand what an alien species would value/need/want beyond to know they were not alone and the curiosity that got them to look to the stars in the first place (just like us).

I hope we find we are not alone, but the math is not that hard to take a very, very big number (every planet out there) and divide that down by 1,000 just say a dozen times or so… to get a very, very small number… 1 or less than 1 (us). I am not saying we are alone, but I am wondering if we are early to the life party (why in a Universe that is only 13.8 billion years old, that easily will last a few trillion years…..why do we think that life should be everywhere in the first 1% of that lifespan? especially once you realize that advanced life happens in a series of very complicated and lucky steps that takes time… lots of time). What if we are just a tiny bit early to the life party for the universe… like what if we are 5 billion years earlier than everyone else. What if there are just 6 advanced civilizations just like earth randomly spread out across the universe right this moment? You know it would take millions of light years to receive a message from one of them if they knew exactly where to send it and we knew exactly how to receive that message. yeah… so….. well for now I will just plan to meet up with everyone on this side at the Great Attractor. Until then, stay insanely curious.

You know, one recurrent sci-fi theme is that everywhere else, people/aliens are slow evolvers and slow thinkers. Maybe by studying the rate of change in our last 200 years worth of broadcasts, those advanced aliens might get scared .. why, they might already be in a race to get here before the Singularity occurs! :-} … I guess early April does this to people :-}

It seems to me that, since a laser beam is focused, we first have to know which planet is looking for us; or send a laser to every planet for which earth is in transit from their view. This number could be “astronomical”.
Also, if laser beams are visible from the side view, as in the illustration for this article, itt broadcasts to every other star that someone here has built lasers.
Am I missing something?

“we first have to know which planet is looking for us”: right, as noted in second footnote. A SETI detection would be the most realistic scenario. I asked the authors to comment on this. Side view is only visible in an atmosphere (due to dust reflection) and at a distant star, the cone would be too large to be visible.

First looking at the headline, my immediate thought was, “That’s the answer to the Fermi Paradox: “Where’s Everbody?”…”Everybody’s hiding.”

But reading the article points out that it will be more of a beacon than a cloak.

Astronomers here are already planning to look for the laser transmissions of other civilizations. Shouldn’t even a tunable laser still send out coherent light that a star would not? It goes without saying that aliens would spot this.

The system the Columbia researchers describe can function as either a beacon or a cloak. It depends on whether the laser sends out steady light (cloaking by blocking the Earth image in front of our Sun) or beacon, by modulating or encoding the laser light. I’ll try to clarify this in the article.

I just noticed your comment on coherent light. I think you’ve just identified a serious weakness of the cloaking scheme; I can’t think of a way to convert to incoherent light and still achieve the vast distances. I’ll ask the astronomers to comment.

The lasers would only replace a tiny percentage of the total light that the aliens would be observing, so the coherence of the lasers would likely be lost in the overall incoherence of the actual star light. Also, if there were 6000 lasers emitting at different wavelengths they would not all be coherent with each other.

“Certainly for our current and upcoming telescopes, such as Kepler and JWST, our cloak would be very effective and the coherent nature of the laser light would be indistinguishable from star light. Coherence, and even light polarization, could give away the game to more advanced detectors, although these are both likely surmountable too with some thought.

“However, a common misunderstanding of our paper is to erroneously assume that we are advocating that humanity should build this for the Earth, but actually we are pointing out that if even our current technology can pull off a pretty effective cloak then other more advanced civilizations may be able to hide from us perfectly.”